In a mechanical seal that seals an annular gap between a rotary shaft and a housing, a sliding interface between a fixed ring provided on a seal cover side fixed to the housing and a rotary ring provided on a collar side fixed to the rotary shaft constitutes a sealing face. In this structure, a biasing member that biases the fixed ring against the rotary ring is provided to maintain the sliding contact between the fixed ring and the rotary ring. Alternatively, a biasing member that biases the rotary ring against the fixed ring is provided in some cases. Consequently, when the mechanical seal is mounted in a predetermined position, the mechanical seal is in a biased state in which a biasing force by the biasing member is acting. Therefore, in order for the mechanical seal to be mounted while being kept in position, some measure is needed. Conventionally, a structure including a sleeve attached to the rotary shaft is used, and a mark is drawn at a position on the surface of the sleeve at which the mechanical seal is to be mounted. However, in this case, the assembly process requires a lot of effort. For this reason, the use of a cartridge-mechanical seal equipped with a set plate that temporarily fixes a seal cover and a collar has been mainstream.
A cartridge-mechanical seal according to a prior art will be described here with reference to FIGS. 6 and 7. FIG. 6 is a front view of a mechanical seal according to a prior art, and FIG. 7 is a schematic cross sectional view showing the mechanical seal according to the prior art in the mounted state. In FIG. 6 a set plate is not illustrated. The cross sectional view of the mechanical seal in FIG. 7 is taken on line B-B in FIG. 6.
The mechanical seal 500 is provided to seal an annular gap between a rotary shaft 200 and a housing 300. The mechanical seal 500 includes an annular seal cover 510 fixed to the housing 300, a fixed ring 520 provided on the seal cover 510 side, an annular collar 530 fixed to the rotary shaft 200, and a rotary ring 540 provided on the collar 530 side. The fixed ring 520 and the rotary ring 540 are adapted to be in sliding contact with each other by their end faces. In order to maintain the sliding contact, a biasing member (spring) 560 that biases the fixed ring 520 against the rotary ring 540 is provided.
The mechanical seal 500 according to the prior art further has a set plate 550 used to temporarily fix the seal cover 510 and the collar 530. The set plate 550 is adapted to be fixed on the outer circumference side of the collar 530 by a bolt 555. Fixing the set plate 550 brings a hook-shaped engagement projection 511 provided on the seal cover 510 and a hook-shaped engagement projection 551 provided on the set plate 550 into engagement with each other, so that the seal cover 510 and the collar 530 are fixed while being positioned with respect to both the axial and radial directions. There are a plurality of such set plates 550 arranged at predetermined circumferential intervals.
With the above-described construction, the mechanical seal 500 can be handled as a single piece as a whole. Thus, in the process of attaching the mechanical seal 500, the mechanical seal 500 constructed as a cartridge is firstly set at a predetermined position. Then, the seal cover 510 is fixed to the housing 300, and the collar 530 is fixed to the rotary shaft 200. Thereafter, the bolts 555 are removed to detach all the set plates 550. As a consequence, the collar 530 and the rotary shaft 540 are made rotatable, while the seal cover 510 and the fixed ring 540 are left fixed on the housing 300.
In the above-described cartridge-mechanical seal 500 according to the prior art, the engagement projection 511 is provided on the seal cover 510, which is the largest part of the mechanical seal 500 and relatively expensive. The seal cover 510 is produced by cutting a cylindrical blank made of a stainless steel. In consequence, the complex shape of the engagement projection 511 requires time-consuming cutting in making the seal cover 510. Moreover, since the engagement projection 511 is a thin part projecting in the axial direction from the seal cover 510, which has a diameter larger than the other parts, the rigidity of the engagement projection 511 tends to be low, leading to breakage during machining in some cases. Moreover, variations in the axial distance among types of the fixed ring 520 and the rotary ring 540 require corresponding variations in the dimension of the engagement projection 511. This leads disadvantageously to low versatility. The above-described situations can lead to an increase in the cost also.